A convenient method for the preparation of oxazaborolidine catalyst in situ using (S)-α,α-diphenylpyrrolidinemethanol, tetrabutylammonium borohydride, and methyl iodide for the asymmetric reduction of prochiral ketones

An oxazaborolidine catalyst is readily prepared in situ at 25 degrees C in THF using (S)-alpha,alpha-diphenylpyrrolidinemethanol and borane generated from tetrabutylammonium borohydride/CH3I reagent system. The oxazaborolidine/BH3 reagent system prepared in this way is useful for the reduction of prochiral ketones to the corresponding alcohols with up to 99% ee. (c) 2006 Elsevier Ltd. All rights reserved.